Kessler and McPhaden, 1995a Abstract
Oceanic equatorial waves and the 1991-93 El Niño
Kessler, W.S. and M.J. McPhaden, 1995
Journal of Climate, 8, 1757-1774, 1995
Equatorial Kelvin and Rossby waves associated with the 1991-93 El Niño
warm event were detected in temperature observations made by the TOGA-TAO
buoy array. Intraseasonal Kelvin waves were a prominent part of equatorial
thermocline depth variability, and were well-represented by a simple model
consisting only of first and second mode baroclinic Kelvin waves. The
second mode was essential to properly represent the observed amplitude.
Thermocline depth variability at 5N and 5S was dominated
by annual and interannual Rossby waves, which were found to have been
largely wind-forced in mid-basin, with little if any signal associated
with eastern boundary reflection. An evaluation of the Wyrtki buildup
hypothesis and the delayed oscillator hypothesis in connection with the
1991-93 events showed that a long lag (about two years) occurred between
the arrival of the downwelling signal in the west and the subsequent
initiation of El Niño; this was considerably longer than suggested by
delayed oscillator theory. No downwelling Rossby wave reflections occurred
at the right time to trigger the onset of the 1991-92 warm event. Termination
of the 1991-92 El Niño was due to an upwelling Rossby wave generated during the height of the warm episode, then reflected from the western
boundary, consistent with delayed oscillator ideas. However, in early 1993,
a second (weaker) warm episode occurred, against the background of a very
anomalously shallow west Pacific thermocline. This shows that the ENSO cycle
cannot be viewed simply as an oscillator mediated by the western boundary
reflection of equatorial Rossby waves, and that a buildup of a thick warm
layer in the west is not a prerequisite to the occurrence of El Niño.
Reprints are available. Contact me at the address below.
Download the paper as it appeared in J.Climate (pdf, 2.2 Mb)
